The present invention relates to a panel type color display device and a system for processing the image information, and more particularly, the invention relates to a panel type color display device of the class wherein there are provided a display portion consisting of a plurality of pixels, of which each is driven in response to the image information to vary the light transmittance thereof, and backlight sources, of which each can be independently on-off controlled in response to the image information to emit a color light in red (R), green (G), or blue (B), and also relates to a system for processing the image information.
In recent years, apparatus for office automation use such as personal computers, and home electronic products like television sets have been made more compact, of lighter weight, and thinner shaped to a great extent. This tendency is reflected in the field of the display device, and causes the same demand for the display device. In order to meet this demand, various efforts are now being paid to develop a flat panel type display device of lighter weight and thinner shape like a liquid crystal display (LCD) as a device capable of being used in place of prevailing conventional CRT""s (cathode ray tubes).
As one of technological demands for these flat panel type display devices, there is a demand for achievement of the full color display. For instance, the color liquid crystal display (LCD) of the thin film transistor system (TFT) realizes the color display by adopting the active matrix system. According to this TFT system, the dot driving is carried out on the dot by dot basis, so that the high duty dot driving can be obtained by making use of the memory effect of condensers respectively associated with dots, thereby providing the LCD that can display color images with excellent contrast. However, this system never fails to require a lot of TFT""s satisfying the VGA specification, thus inevitably resulting in not only pushing up the manufacturing cost, but also lowering the manufacturing yield. Further, what is worse, this point is still remaining as an unsolved problem up to now without finding any effective solution.
On one hand, the super twisted nematic system (STN) has succeeded in realizing a low cost color LCD by means of adopting the simple matrix system. In this case, however, the speed of frame display is not so fast that color mixture is apt to take place, thus still leaving the problem to be solve as to its poor contrast. In order to solve this problem and to realize the color display with fine contrast at the high-speed frame display, there have been proposed various driving systems as countermeasures for obviating such problem, for instance the double matrix electrode driving system, the time sharing driving system, and so forth. Furthermore, there have been proposed the active addressing driving system that tries to realize the fine contrast and the high-speed frame display without reducing the resolution, by dispersing small pulses instead of large selecting pulses and performing simultaneous scanning of all the lines.
Regardless of the TFT system or the STN system, most of conventional LCD""s are adopting a color filter system comprising filters of 3 primary colors R, G, and B. In case of displaying in color R, the region for color R is made light transmissible while the other regions for G and B are made not. In case of the color filter system, however, as will be easily understood, respective color regions of R, G, and B require proper pixels corresponding thereto, so that 3 times pixels of the monochromatic display have to be driven for full color display. Therefore, in order to obtain an image with high resolution, there are required the finest precision machining, the sophisticated technology for driving pixels, and the color filters having the improved light transmittance. Moreover, there has to be solved the difficult issue of color balance adjustment in the display. As mentioned above, there are embraced in the color filter system a lot of problems that have to be obviated by solving thereof.
In view of the situation of the prior art LCD as described in the above, there has been recently proposed such a panel type color LCD adopting the 3 color backlight system as disclosed in JPA No. Hei 4 (1992)-338996. In the color LCD of this type, there are provided 3 independent light sources of which each is specifically assigned to emit a color light of R, G, or B, and is turned on in order at a predetermined period. Thus, the full color display can be obtained by applying color signals to corresponding pixels in synchronization with said period of turning on the light sources.
According to the conventional color filter system, it is possible to process color signals of R, G, and B as parallel data. For instance, if it is desired to display the image of high brightness with the R-signal, regardless of behaviors of G or B signals, it is possible to overwrite the image data on the R region of pixels by making use of the memory effect due to the condensers of the LCD driving circuit. Thus, the color video can be easily obtained with high contrast.
However, according to the 3 color backlight system, the color image information is once converted into the serial data in which the image information corresponding to respective colors R, G, and B, are switched at a predetermined period, and then, the backlight sources of R, G, and B, are sequentially turned on in synchronization with the switching period of said serial data, thereby realizing the full color image display. Therefore, as shown in FIG. 11, even though it is desired to obtain the image of high brightness with the R-signal and the liquid crystal in a predetermined pixel region is driven with said R-signal to turn it on, this ON-state of the liquid crystal with R-signal is soon erased by the G-signal or B-signal in the next period, so that it is hardly possible to obtain the adequately high quantity of the transmitting light, thus the color image with high contrast being not obtainable. Especially, this operational characteristics remarkably appears in case of realizing the color display by means of the STN system, so that it has been very much desired to promptly solve this problem.
The present invention has been made in view of the various problems as described in the above, which would never fail to come out in the course of realizing the panel type color display according to the 3 color backlight system. Accordingly, an object of the present invention is to provide a novel and improved panel type color display device which is most suitably adaptable especially to the LCD of the STN system, and in which signals for driving pixels are so improved that the frame response of respective pixels is enhanced and the color image can be obtained with high contrast.
Another object of the present invention is to provide a novel and improved panel type color display device in which the image information is developed at a high speed, and the speed of transmitting information to the LCD is made much faster.
In order to solve the problems as described above, the present invention provides a novel and improved display device of 3 color backlight system in which there are provided a display portion consisting of a plurality of pixels which are driven in response to the image information to vary the light transmittance thereof, and backlight sources of which each can be independently on-off controlled and is assigned to emit a color light of R), G, or B.
According to an aspect of the invention, there is provided a novel and improved display device wherein there are provided means for converting the color image information into the serial data in which the image information corresponding to respective colors R, G, and B is sequentially switched at a predetermined time period; means for converting said serial data of colors R, G, and B in said respective time periods into the plotting data of colors R, G, and B for use in driving a plurality of pixels existing within a predetermined range; and means for repetitively driving a plurality of pixels existing in said predetermined range within said respective time periods based on said plotting data of colors R, G, and B. In this case, it is preferable that said display device further is provided with means for controlling the number of repetitively driving a plurality of pixels existing in said predetermined range within said respective time periods in correspondence with the gradation information that is obtained from said image information.
According to another aspect of the invention, there is provided a novel and improved display device wherein there are provided means for converting the color image information into the serial data in which the image information of respective colors R, G, and B is sequentially switched at a predetermined time period; a first data bus means for parallelly developing the serial data of colors R, G, and B within said respective time period into the serial data of L (integer); a memory means for storing the plotting data of L of which each consists of the pixel information of Mxc3x97N (integer) by simultaneously writing the parallel data of L corresponding to each pixel to the addresses of L; means for selecting the plotting data of K (integer) from said plotting data of L; a second data bus means for reading out the selected plotting data of K from said memory means by the pixel information of M at a time in installments of N; and means for driving the pixels of Mxc3x97N existing in a predetermined range K times within said time period by means of the plotting data of K as read out. In this case, the selecting means can determine the number K of repetitively selecting said plotting data in correspondence with the gradation information as obtained from said image information.
Further, according to another aspect of the present invention, there is provided a novel and improved display device wherein there are provided means for converting the color image information into the serial data in which the image information of respective colors R, G, and B is sequentially switched at a predetermined time period; a first data bus means for parallelly developing the serial data of colors R, G, and B within said respective time period in the number L (integer) of all the gradations as requested; a memory means for storing the plotting data of L (integer) consisting of the pixel information of Mxc3x97N (integer), by simultaneously writing the parallel data of L corresponding to each pixel to the addresses of L; means for selecting the plotting data of K (integer) from said plotting data of L; a second data bus means for reading out the plotting data having the gradation number (K) requested to the plotting data to be read out from said memory means by the pixel information of M at a time in installments of N; and means for driving the pixels of Mxc3x97N existing in a predetermined range K times within said time period by means of the plotting data of K as read out.
Still further, according to another aspect of the present invention, there is provided a system for processing the image information wherein at the time of processing the image information through a memory having at least 3 addresses of which areas are different from one another, only all the addresses in the data area to be parallelly developed are made effective while the data designated by remaining addresses are parallelly processed. In this case, the data area of which all the addresses are to be made effective, is made different depending on whether the operation is for writing the data in or reading out the same.
For instance, according to the present invention, composite signals according to the system of NTSC (National Television System Committee) are divided into color data of colors R, G, and B, and then, these color data are converted into the serial data that are sequentially switched at a predetermined time period. Now, let us explain here the operation of the present invention by taking the case of R-signals. In case of plotting an image on a screen consisting of 640xc3x97480 dots for instance, be exciting said dots with the R-signals contained in respective time periods of said serial data, the screen is divided into two parts i.e. upper and lower parts, and there are formed the plotting data of R-color for 640xc3x97240 dots each. Pixels existing in said range and consisting of one or some dots are repetitively driven within respective time periods by means of this plotting data, thereby enabling the liquid crystal to largely respond to the signals to obtain the liquid crystal image display with high brightness. The brightness of the image is adjusted by regulating the number of repetitively driving the pixels, so that if the high brightness is necessary, it may be attained by increasing said number of repetitively driving pixels, and if lower brightness is enough, it may be done by decreasing the same. In this way, it becomes possible to give difference in color gradation of the image, thus the image appearing with high contrast.
Explaining more in detail the above, said R-signals converted into the serial data in the manner as described above are parallelly developed through a first data bus corresponding to the number of all the gradations as requested (e.g. L=256). These 256 data are separately stored in respective gradation addresses of the memory, thereby 256 plotting data of R-color being formed for the screen area of 640xc3x97240 dots. In the next, after forming the plotting data in the memory like the above, the data for 640 dots are read out at a time in response to a line address, and this is repeated 240 times with regard to respective line addresses. Accordingly, it is natural that the readout speed becomes much higher comparing with the prior art sequential readout system, which reads out one R-color plotting data for one dot at a time and repeats it 640xc3x97240 times. Further, according to the present invention, the R-color plotting data as read out with such high speed are repetitively read out plural times (256 times max.) over the time of T/256 (T: total time). Accordingly, even if the total time (T) is equal, the liquid crystal responding quantity having much wider dynamic range can be obtained comparing with the prior art system, in which the pixel is driven only one time over the total time T. Accordingly, it is possible to obtain the image with higher contrast comparing with the prior art system. The difference in gradation can be expressed by selecting the number of repetitively driving pixels, for instance 256 times driving for expressing all the gradation and 128 times driving for expressing a half of gradation.
According to the system for processing the image information of the present invention, there are provided the RAM groups which are able to store the display information on the respective pixels, which are managed by the line address and the data select address, after graduating said information by the gradation address as the display data having different gradations. Accordingly, as typically shown in FIG. 10, in the time of writing operation, all the gradation addresses are made effective, and the data of 8 bits are decoded and developed in the data buses of 256, for instance. After this, the writing for 256 bits is parallelly carried out to the respective gradation addresses according to designations by the line addresses (0xcx9c239) and the data selector addresses (0xcx9c639) as well. Contrary to this, in the time of readout operation, all the data selector addresses are made effective, and the display data for each line are parallelly read out based on the appointment by the gradation addresses (0xcx9c255) and the line addresses (0xcx9c239) as well.
As has been discussed in the above, according to the system of the present invention, 3 kinds of addresses in different areas are combined in correspondence with a sort of the operation, and all the addresses in the data area to which the data are to be developed, are made effective, thereby enabling a lot of data to be simultaneously processed at a single clock timing. Therefore, there can be attained the high-speed information transmission to the liquid crystal display and the high-speed response in driving the same.